Mimicry: Things are not always as they seem

I recently posted the photo above, along with the message below, to Facebook:

A friendly public service announcement on behalf of America's flower flies (family Syrphidae). Those little bee-like insects (such as in the photo) that sometimes land on you are not bees. They are valuable, pollinating flies that do a good job of mimicking bees. While they do have a tendency to land on people's skin - seeking minerals in your sweat - they cannot sting, bite or otherwise hurt you. Pancaking them, or dousing one's self with insect repellent is not necessary. I only say this because I've seen about six people in the last week overreacting to the "aggressive bees".

Apparently it was of help to the flies, as the message got a lot of attention. This experience got me to thinking about the broader picture of mimicry, one of my favorite subjects in all of natural history. The flower fly (or hover fly) does a darn good job at looking like something that might sting, thus theoretically dissuading would be predators from attacking. But flower flies are just the tip of the iceberg when it comes to insects mimicking the appearance of Hymenoptera (bees and wasps) that pack a punch.

A few examples follow...

A homicidal looking "bumblebee" if there ever was one. This is a robberfly, Laphria thoracica, sitting on a conspicuous perch awaiting insect prey to fly by. When a suitable victim makes an appearance, the fly will whir out after it, grab the meal to be with spiny legs, and stab it with a syringelike proboscis. The fly then injects chemicals that paralyze the victim and speed in the decomposition of its innards, the latter of which will eventually sucked out via the fly's proboscis.

Why look like a bumblebee? Possible because robberflies are prone to perching out in the open, and looking like something that stings may telegraph a message of AVOID to birds.

If you weren't privy to this one, it'd make you head the opposite direction, perhaps. This is a very large fly known as a Mydas Fly, Mydas clavatus. They greatly resemble large predatory spider wasps, but are completely harmless. Their larvae dwell in decomposing wood and are predators of beetle larvae. The ferocious looking wasp-mimicking adult flies apparently only take nectar from flowers.

The first time I saw a Thick-headed Fly in the genus Physocephala (I think this is P. tibialis), it completely fooled me. I was sure it was a wasp. It has a waspish "waist" and thickened terminal abdomen, and even waves its front legs around when perched in the manner of some wasps. This species is reportedly a parasitoid of the bumblebee Bombus bimaculatus.

Beetles are in on the let's look like something dangerous act, too. This is an Amorpha Borer, Megacyllene decora, and the adults really look like a hornet, especially in flight.

This one may take the cake, if we're interpreting the disguise properly. It is another beetle, the Delta Flower Scarab, Trigonopeltastes delta. John Howard introduced me to this beauty, which if you are lucky, can be found visiting flowers such as this rattlesnake-master, Eryngium yuccifolium. John noted that when the beetle is flushed, it flares its wings in such a way that the pattern forms a large scary wasplike face - two big brown eyes and white mandibles below those. Hmmm...

Another great hornet mimicking beetle, the Locust Borer, Megacyllene robiniae, which is common on goldenrods in fall.

Even moths - yes, MOTHS! - get in on the act. This is the Eupatorium Borer, Carmenta bassiformis (I believe). It, and its fellow borers in the family Sesiidae are fabulous actors, greatly resembling bees and wasps.

A Squash Vine Borer, Melittia cucurbitae, visits the flowers of dogbane, Apocynum cannabinum. This day-flying moth would fool just about anyone into thinking it is some sort of wasp. It even dangles is its legs, which are thickened with brushes of hair, as it flies just as many wasps do.

Here we have a dragonfly, of all things, seemingly mimicking the look of a bee/wasp/hornet sort of thing. This is a female Elfin Skimmer, Nannothemis bella, the smallest dragonfly in North America. Only the female apparently employs the mimicry; males look very different. She even twitches her abdomen when at rest, in the manner of some bees. When seen in the field, the effect is strikingly wasplike.

Finally, at the end of this short list of mimicry examples is the utterly bizarre mantisfly known as Climaciella brunnea. Squint your eyes a bit and ignore some of the odd appendages, and this thing is the spitting image of paper wasps in the genus Polistes. These wasps certainly pack a punch, and I'd imagine potential predators learn a painful lesson if they try and capture and eat them. If you can look like a paper wasp, a la this mantisfly, they'll presumably leave you alone too. Mantisflies are a story in their own right, and I've written about them HERE.

Sometime I'll have to write about all the creatures that mimic bird droppings.

The remarkable world of mimicry

One of Nature's most interesting facets is mimicry. The natural world is loaded with animals that are not what they appear to be. This deception gives the imitators an advantage, whether it be predator avoidance, ease of capturing prey, camouflage, or some other edge. Through the miraculous fits and spurts of evolution, the mimickers have developed disguises that are often incredibly similar to quite unrelated animals.

Even though mimicry is one of the greatest examples of Darwinian natural selection at work, Darwin himself missed the entire subject. It goes unmentioned in his landmark The Origin of Species. It was English scientist Henry Bates who brought mimicry to the forefront as an outstanding example of Darwinian evolution, shortly after Darwin's book was published in 1859. Far from being jealous or bent out of shape by Bates' elucidation of mimicry, Darwin became a great admirer and went so far as to say "I have just finished, after several reads, your paper. In my opinion it is one of the most remarkable and admirable papers I ever read in my life.... I rejoice that I passed over the whole subject in the Origin, for I should have made a precious mess of it".

Last Saturday, David Wagner, myself and a few others were able to make a two hour foray through an eastern Pennsylvania park. It was a nice place, but certainly nothing out of the ordinary. Meadows buffered by a corn field, some woods and a stream, and brushy edge habitats. We still managed to find some interesting animals, including the mimics that follow.

A small ant forages along the surface of a leaf. But wait - something looks amiss.

This is no ant! Count the legs. It's a spider, doing a remarkably good job of looking like an ant. This is one of a group of jumping spiders that are ant mimics, and very good ones at that. I believe this one is Synemosyna formica, but I will stand to be corrected if someone knows better.

The ant mimic jumper is about the size of an average ant, and typically moves along the ground, often with ants. It's resemblance to the totally unrelated insects (spiders aren't even insects, they're arachnids) is startling. It may be that the spider gains an advantage by looking like something that potential prey might tend to ignore. Or it may be that potential predators of the spider often find ants distasteful and shun them.

A spotted thyris, Thyris maculata, forages on the flowers of common milkweed. Were this little day-flying moth not actively feeding, it would have been quite hard to see.

This moth and many of its ilk are fabulous leaf mimics, or have otherwise evolved patterns and shapes that resemble plant parts. When this thyris is at rest on leaves or other plant parts that match it, your chances of spotting it are slim to none, and presumably that holds true for beasts that would like to eat it.

We were quite pleased to encounter this insect, which is an awesome example of mimicry and one to watch for in your own local patch. To the casual eye, it would appear to just be a large fuzzy bumblebee at rest on a leaf. But the trained observer will hone in on this bug right away, as there are several things amiss. For one, bumblebees very seldom stop and bask on leaves like this. If the weird behavior stimulates a closer inspection, you'll quickly see that the insect has huge eyes and only two wings - the hallmarks of a fly.

This is one of the robber flies in the genus Laphria (thanks to Benjamin Coulter for the species specific ID of Laphria thoracica) and they are consummate bee mimics. Robber flies are barbaric predators that typically hunt from perches such as this leaf. They wait and watch, and when a suitable victim happens by, the robber fly darts out, grabs it, and stabs the prey with that syringelike proboscis that can be seen projecting from the mouthparts. The fly then injects chemicals that cripple the victim, and dilute its innards. After suitably stewing the prey, the robber fly sucks it dry via the proboscis.

Note how the hairs of the upper legs and proboscis tip are shaded in yellow-orange, making them look just like pollen-dusted bumbebee hairs. Incredible. The selective advantage gained by resembling a bumblebee may be predator avoidance. Birds, which might be the most likely animals to bag a robber fly, may well avoid bumblebees in most cases, as they'll know they could receive a painful sting. Thus, the fly is free to loaf conspicuously on perches and scan for prey.